Method for converting a non-driven tag axle system to a driven axle system

ABSTRACT

A method for converting a non-driven tag axle system to a driven axle system is disclosed where a forward driven axle system is converted to drive an interaxle drive shaft. The interaxle drive shaft is connected to a drive axle head mounted within the tag axle housing. Drive axles are connected to drive axle head. In another embodiment, a forward driven axle system is removed from a first position on the vehicle frame and the tag axle is removed from a second position on the vehicle frame. A differential is installed in the tag axle and it is located in the first position. The forward driven axle system is located in the second position and connected to the differential in the first position.

FIELD OF THE INVENTION

The present invention relates to method of converting a non-driven tagaxle system to a driven axle system in a tandem axle system.

BACKGROUND OF THE INVENTION

Single drive axle trucks with a tag axle are known for their lighterweight, improved fuel economy, low installation cost and reliability inoperations over tandem drive axle configurations. The North Americantruck market, however, is dominated by the tandem drive axleconfiguration in part due to single drive axle trucks having a lowresale value. The low resale value can be partly attributed to the highcost associated with converting a single drive axle truck to a tandemdrive axle truck. Conversion costs can be high since current tag axleshave a different profile and wheel equipment than the drive axle, thusrequiring a retrofitter to discard the tag axle, the suspensionbracketry and the wheel equipment and install a new drive axle,suspension bracketry and wheel equipment.

In light of the disadvantages of the prior art, it would be advantageousto convert a non-driven tag axle to a driven axle by re-using much ofthe original equipment of the vehicle. It would also be advantageous toprovide the vehicle with a tag axle assembly and a driven axle assemblythat have substantially identical profiles that they can be interchangedwith one another. It would also be advantageous for a truck fleet ownerto have the ability to purchase a single drive axle truck and then laterconvert it to a tandem drive axle truck for resale.

SUMMARY OF THE INVENTION

The present invention is directed toward a method for converting asingle drive axle vehicle to a tandem drive axle vehicle. The methodincludes providing a tag axle system comprising a tag axle housing, aremovable cover plate attached to the tag axle housing and a pair ofhollow, radially extending arms with a closure in each arm. A forwarddriven axle system is also provided comprising a forward axle assemblylocated in a forward axle housing and driving a stub shaft assembly. Theaxle housing has a closure in an output shaft aperture. The forward axleassembly is replaced, including the stub shaft assembly, with a forwardrear axle assembly. The cover plate of the tag axle housing is removedand a drive axle head assembly is installed into the tag axle housing.The closure in the output shaft aperture is removed and an output shaftis installed through the aperture. The output shaft is connected betweenthe forward rear axle assembly and the drive axle head assembly.Additionally, the closures in each arm of the tag axle system areremoved and axles connected to the drive axle head assembly areinserted.

The present invention is also directed toward an additional method ofconverting a single drive axle vehicle to a tandem drive axle vehicleincluding providing a tag axle and a driven axle of a tandem axlesystem, where the tag axle comprises a bowl having two hollow, radiallyextending arms. The driven axle is connected to an engine with arotatable drive shaft. The tag axle is removed from a rear position onthe vehicle frame and a differential assembly is mounted within the bowlof the tag axle. A left axle shaft and a right axle shaft are installedwithin the hollow arms and the shafts are connected to the differentialassembly. The driven axle is removed from the front position on thevehicle frame. The tag axle, with the differential assembly and the leftand right axle shafts, is installed in the front position on the vehicleframe and the differential assembly is attached to the drive shaft. Thedriven axle is then installed in the rear position on the vehicle frameand connected to the differential of the tag axle.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other advantages of the present invention, willbecome readily apparent to those skilled in the art from the followingdetailed description when considered in the light of the accompanyingdrawings in which:

FIG. 1 is a schematic view of a drive axle system and a tag axle systemof the present invention;

FIG. 2 is side view of an original component of the drive axle system;

FIG. 3 is a side view of the component of FIG. 2 modified according tothe present invention;

FIG. 4 is an exploded, schematic view of some of the components used tomodify the component of FIG. 2;

FIG. 5 is an exploded, schematic view of some of the components used tomodify the drive axle system of FIG. 2;

FIG. 6 is a schematic, perspective view depicting a step of the presentinvention;

FIG. 7 is a schematic, perspective view depicting yet another step ofthe present invention;

FIG. 8 is a schematic, perspective view of a drive axle system and a tagaxle system of an alternative embodiment of the present invention;

FIG. 9 is a schematic, perspective view of a step of the process of thealternative embodiment of the present invention; and

FIG. 10 is a schematic, perspective view of yet another step of theprocess of the alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood that the invention may assume various alternativeorientations and step sequences, except where expressly specified to thecontrary. It is also to be understood that the specific devices andprocesses illustrated in the attached drawings, and described in thefollowing specification are simply exemplary embodiments of theinventive concepts defined in the appended claims. Hence, specificdimensions, directions or other physical characteristics relating to theembodiments disclosed are not to be considered as limiting, unless theclaims expressly state otherwise.

Referring now to FIG. 1, a tag axle system 20 having a tag axle housing22, a removable cover 24 attached to the tag axle housing 22 and a pairof hollow, radially extending arms 26 secured to the housing 22 isdepicted. In the preferred embodiment, at least two closures 28 arelocated in each arm 26 to prevent, or reduce, lubricant from escaping.The closures 28 are preferably removeable from each arm 26.

At least one wheel (not shown) is rotatably attached to an outboardportion 30 of each radially extending arm 26. At least one tire (notshown) is mounted on the at least one wheel, as known by those skilledin the art.

FIG. 1 also depicts a forward driven axle system 32 having a forwardaxle differential assembly 34 located in a forward axle housing 36.Preferably, the forward axle housing 36 has an aperture 38 located in arear covering 40. A selectively removeable closure 42 is fitted withinthe aperture 38 of the rear covering 40.

The forward driven axle system 32 has a pair of hollow, radiallyextending arms 44 secured to the housing 36 that rotatably house a firstaxle shaft 46 and a second axle shaft 48. A first end 50 of the firstaxle shaft 46 is drivingly connected to the forward axle differentialassembly 34. A first end 52 of the second axle shaft 48 is drivinglyconnected to the forward axle differential assembly 34. A second end 54of the first axle shaft 46 has at least one wheel (not shown) rotatablyattached thereto. At least one tire (not shown) is mounted to the wheelas known by those skilled in the art. A second end 56 of the second axleshaft 48 has at least one wheel (not shown) rotatably attached thereto.At least one tire (not shown) is mounted to the wheel, as known by thoseskilled in the art.

One embodiment of the forward axle differential assembly 34 is depictedin FIG. 2. In the depicted embodiment, the forward axle differentialassembly 34 is a high entry forward axle assembly, as known to thoseskilled in the art, although other axle assemblies are within the scopeof the present invention. The forward axle differential assembly 34 ishoused within a differential case 58. The case 58 may be constructed ofa single piece or it may be constructed of multiple pieces joinedtogether by a plurality of bolts. A differential carrier cover 60 istypically also secured to the differential case 58.

A stub shaft 62 is rotatably mounted within the differential case 58 onat least a first bearing 64 and a second bearing 66. The first bearing64 is secured between a bearing cone 68 and a bearing cup 70 and thesecond bearing 66 is secured between a bearing cone 72 and a bearing cup74. Additional bearings, bearing cups and bearing cones, or otherantifriction means known to those skilled in the art are well within thescope of the present invention.

An input adjuster cup assembly 76 is provided adjacent the first bearing64 for adjusting the position of the bearing 64 as known to thoseskilled in the art. A lubricant seal 78 is located axially adjacent theinput adjuster cup assembly 76 for preventing lubricant from escapingfrom the differential case 58.

The stub shaft 62 is rotatably connected to a helical pinion gear 80.The helical pinion gear 80 is rotatably mounted within the differentialcase 58 by at least a third bearing 82 and a fourth bearing 84. Thethird bearing 82 is secured within a bearing cup 86 and a bearing cone88 and the fourth bearing 84 is secured within a bearing cup 90 and abearing cone 92. The helical pinion gear 80 is rotatably connected to aring gear 94. The helical pinion gear 80 can be aligned with therotational axis 96 of the ring gear 94 or it may be offset from therotational axis 96 of the ring gear 94, as depicted in FIG. 2.

The first axle shaft 46 and the second axle shaft 48 are connected tothe ring gear 94 with a plurality of side gears (not shown), as known tothose skilled in the art. The first and second axle shafts 46, 48 arerotationally mounted within the differential case 58 on at least twobearings (not shown).

According to a preferred embodiment of the method of the presentinvention, the forward axle differential assembly 34 is converted to aforward rear axle differential assembly 100 by removing the stub shaft62 and installing an input shaft 102 and interaxle differentialcomponents, as shown in FIG. 3, in its place. A new lubricant seal 104,input adjuster cup assembly 106 and first bearing 108, with a newbearing cone 110 and bearing cup 112, are preferably installed, althoughin some circumstances the originals may be reused unless they are wornor otherwise damaged.

A second lubricant seal 114 is added adjacent a lock out clutch 116, asbest seen in FIG. 3. The clutch 116 is slidingly mounted a plurality ofsplines 118 located on a raised diameter portion 120 of the input shaft102. The clutch 116 has a plurality of circumferentially disposed teeth122 which selectively engage with a corresponding set of teeth 124 on anadjacent helical side gear 126. The teeth 122 on the clutch 116 areurged into engagement with the teeth 124 on the helical side gear 126 bya shift fork 128, best seen in FIG. 4, that moves the clutch 116 in afirst axial direction. The shift fork 128 is axially translated by afluid driven piston 130 which is moved in response to a fluid pressureshift signal. A piston cover 132 and piston o-ring 134 are secured tothe piston 130 for sealingly enclosing at least a portion of the piston130. At least one coil spring 136, in contact with the shift fork 128,urges the shift fork 128 in a second axial direction, opposite the firstaxial direction.

Those skilled in the art will appreciate that engaging the teeth 122 onthe clutch 116 with the teeth 124 on the helical side gear 126 willengage an interaxle differential assembly 138, depicted in FIG. 3. Ifthe clutch 116 and the side gear 126 are not engaged, the power from theinput shaft 102 will be transmitted to the axle behind the forward rearaxle differential assembly 100. The clutch 116 allows power to beselectively provided to the axle with the most available wheel traction.

The interaxle differential assembly 138 has a spider 140 connected tothe input shaft 102. The spider 140 has at least a pair of oppositelydisposed differential gears 142 which on one side engage with an outputside gear 144 and on the other side engage with the helical side gear126. The output side gear 144 is connected to an output shaft 146, bestseen in FIG. 5. A bearing assembly comprising of at least one bearingring 148, at least one bearing cup 150 and at least one bearing cone 152are located about the output shaft 146 to facilitate its rotation. Theoutput shaft 146 is connected to an output yoke 154.

The output yoke 154 is connected to a first end 156 of an interaxledrive shaft 158, as shown in FIG. 6. A second end 160 of the interaxledrive shaft 158 is connected a drive axle head assembly 162 that hasbeen located within the tag axle housing 22. The drive axle headassembly 162 is located within the tag axle housing 22 by removing thecover 24 on the original tag axle system 20 and positioning the assembly162 within the housing 22, as shown in FIG. 7. Referring back to FIG. 6,the drive axle head assembly 162 provides drive to wheels (not shown)supported on either side of the assembly 162 on a first axle shaft 164and a second axle shaft 166 located within a first radially extendingarm 168 and a second radially extending arm 170, respectively. A firstclosure 172, located in the first radially extending arm 168 to preventwheel bearing lubricant from entering the tag axle housing 22, isremoved prior to installation of the first axle shaft 164. A secondclosure 174 located within the second radially extending arm 170, alsopresent to prevent wheel bearing lubricant from entering the tag axlehousing 22, is removed prior to installation of the second axle shaft166. The assembly 162 may include a pinion assembly 176 and adifferential gear assembly 178, as known to those skilled in the art fordriving a rear axle of a tandem axle system.

The pinion shaft assembly 176 is provided to transfer torque from theinteraxle drive shaft 158 to the differential gear assembly 178. Thedifferential gear assembly 178 allows the wheels supported on eitherside of the axle assembly 178 to rotate at different speeds. Theassembly 178 includes a pinion gear (not shown), a ring gear 182 and aconventional bevel gear set (not shown). The pinion gear transferstorque from the interaxle drive shaft 158 to the ring gear 182. The ringgear 182 transfers torque from the pinion gear to the bevel gear set andis convention in the art.

The tag axle system, described above, is then located back in itsoriginal position behind the first axle 46 on a frame 186, as shown inFIG. 6. Those skilled in the art will appreciate that torque provided bya prime mover, such as an internal combustion engine (not shown), istransferred to the input shaft 102 of the forward rear axle differentialassembly 100. The torque is divided within the forward rear axledifferential assembly 100 for driving the wheels associated therewithand part of the torque is transferred to the interaxle drive shaft 158.The interaxle drive shaft 158 transmits torque to the drive axle headassembly 162 which in turn drives the wheels associated therewith.

An alternative embodiment of the present invention is depicted in FIG. 8and comprises a tag axle system 188 located behind a driven axle system190 of a tandem axle system 192. The driven axle system 190 is mountedin a first position 194 on a vehicle frame 196 and the tag axle system188 is located in a second position 198 behind the first position 194 onthe vehicle frame 186.

The driven axle system 190 has a bowl 200 with two radially extendingarms 202 connected thereto. Axle shafts 204 are located within each ofthe radially extending arms 202. The axle shafts 204 are drivinglyconnected to a differential 206 housed within the bowl 200 of the drivenaxle system 190. The driven axle system 190 is connected to a primemover, such as an internal combustion engine (not shown), with arotatable drive shaft 208. The tag axle system 188 has a bowl 209originally fitted with no differential and two substantially hollow arms211 that radially extend from the bowl 209. Preferably, the tag axlesystem 188 has a substantially similar shape and size as the driven axlesystem 190.

Looking now at FIGS. 8 and 9, the driven axle system 190 is removed fromits first position 194 on the frame 196 and the tag axle system 188 isremoved from its second position 198 on the frame 196. A cover 210 onthe bowl 209 of the tag axle system 188 is removed and a forward rearaxle differential assembly 212 is installed within the bowl 209. In thepreferred embodiment, the bowl 209 has been pre-machined to accept theforward rear axle differential assembly 212.

The forward rear axle differential assembly 212 is adapted to drivewheels (not shown) supported on either side of the differential assembly212. Preferably, the forward rear axle differential assembly 212 isidentical to, or very similar to, the high entry forward rear axledifferential assembly 100 described above. Those skilled in the art willappreciate that other forward rear axle differential assemblies, otherthan as described above, may be used in order to provide an assemblydesigned for a specific application.

The former tag axle system 188, having a forward rear axle differentialassembly 212 installed therein, will now be referred to as a forwardrear assembly 214 and is depicted as such in FIG. 10. A first end 216 ofa first axle shaft 218 is connected to the forward rear axledifferential assembly 212 within one radially extending arm 202, asknown by those skilled in the art. A first end 220 of a second axleshaft 222 is connected to the forward rear axle differential assembly212 within the other radially extending arm 202, also as known by thoseskilled in the art. A second end 224 of the first axle shaft 218 isconnected to a first wheel (not shown) and at least one associated tire(not shown). A second end 226 of the second axle shaft 222 is connectedto a second wheel (not shown) and at least one associated tire (notshown). The forward rear assembly 214 is installed in the first position194 on the frame 196.

An output shaft (not shown) of the forward rear axle assembly 214 isconnected, as described above, to an output yoke (not shown). The outputyoke is connected to a first end 232 of an interaxle drive shaft 234.

The former driven axle system 190, removed from the first position 194on the frame 196, will now be referred to a rear rear assembly 236, asit is depicted in FIG. 10. The rear rear assembly 236 is installed inthe second position 198 on the frame 196. A second end 238 of theinteraxle drive shaft 234 is drivingly connected, in a manner known bythose skilled in the art, to the differential 206 within the rear rearassembly 236.

While it is preferred to reuse the same differential 206, axle shafts240 and wheels (not shown) of the rear rear assembly 236, those skilledin the art will appreciate that modifications to one or any of theseitems can be easily accomplished during the installation of the rearrear assembly 236. Those skilled in the art will also appreciate thatsuspension bracketing may be secured to either the rear rear assembly236 or the forward rear assembly 214 as required.

Those skilled in the art will appreciate that based upon the descriptionof the invention above, driving torque from an internal combustionengine (not shown) is transmitted from the rotatable drive shaft 208 andinto the forward rear assembly 214. The forward rear axle differentialassembly 212 divides the torque and provides a portion of the torque tothe first and second axle shafts 218, 222 to drive the wheels (notshown) and tires (not shown) associated therewith. The remainder of thetorque is transmitted through the forward rear axle differentialassembly 212 to drive the interaxle drive shaft 234. The rotation of theinteraxle drive shaft 234 drives the differential 206 of the rear rearassembly 236. The differential 206 of the rear rear assembly 236provides torque to a first axle shaft 242 and second axle shaft 244 todrive the wheels (not shown and tires (not shown) associated therewith.

In accordance with the provisions of the patent statutes, the presentinvention has been described in what is considered to represent itspreferred embodiments. However, it should be noted that the inventioncan be practiced otherwise than as specifically illustrated anddescribed without departing from its spirit or scope.

1. A method for converting a non-driven tag axle system to a driven axlesystem, comprising: providing a tag axle system comprising a tag axlehousing, a removable cover plate attached to said tag axle housing and apair of hollow, radially extending arms with a closure in each arm;providing a forward driven axle system comprising a forward axleassembly located in a forward axle housing and driving a stub shaftassembly, said forward axle housing having a closure in an output shaftaperture; converting said forward axle assembly to a forward rear axleassembly; removing said cover plate of said tag axle housing andinstalling a drive axle head assembly into said tag axle housing;removing said closure in said output shaft aperture and installing anoutput shaft through said aperture and connecting said output shaft withsaid forward rear axle assembly and with said drive axle head assembly;and removing said closures in each arm and inserting axles forconnection with said drive axle head assembly.
 2. The method of claim 1,wherein said forward axle assembly is a high entry single drive forwardaxle assembly.
 3. The method of claim 1, wherein said closures in eachof said tag axle housing arms are selectively removeable fluid tightplugs fitted within each of said arms.
 4. The method of claim 1, saidforward axle assembly is converted to a forward rear axle assembly byremoving said stub shaft assembly and installing at least a side gear,an interaxle differential assembly and an input shaft.
 5. The method ofclaim 1, wherein said forward axle assembly is converted to a forwardrear axle assembly by installing an interaxle differential lockmechanism to said forward axle assembly.
 6. The method of claim 1,wherein said forward axle assembly is converted to a forward rear axleassembly by installing a shift fork and push rod assembly.
 7. The methodof claim 1, wherein said forward axle assembly is converted to a forwardrear axle assembly by installing a piston assembly.
 8. A method forconverting a non-driven tag axle to a driven axle, comprising: providinga tag axle system; converting a forward driven axle system to a forwardrear axle assembly by at least installing a side gear, an interaxledifferential assembly, an input shaft, an interaxle differential lockmechanism, a shift fork and push rod assembly and a piston assembly;installing a drive axle head within said tag axle system; and connectingan output shaft between said forward rear axle assembly and said driveaxle head.
 9. The method of claim 8, wherein said tag axle systemincludes a tag axle housing, a removable cover plate attached to saidtag axle housing and a pair of radially extending arms with a closure ineach arm.
 10. The method of claim 8, wherein said forward driven axlesystem is converted to a forward rear axle assembly by removing a stubshaft assembly from said forward driven axle system.
 11. The method ofclaim 8, wherein said forward driven axle system is converted to aforward rear axle assembly by removing a closure from an aperturelocated in a forward axle housing and locating said output shaft throughsaid aperture.
 12. The method of claim 9, wherein said closures locatedwithin said radially extending arms of said tag axle system are removedand replaced with at least two axles shafts connected to drive axlehead.
 13. A method for converting a non-driven tag axle system to adriven axle system, comprising: providing a tag axle system and a drivenaxle system of a tandem axle system, said driven axle system beingconnected to a rotatable drive shaft; removing said tag axle system froma rear position in a vehicle frame; mounting a differential assemblywithin said tag axle system; connecting a first axle shaft and a secondaxle shaft to said differential assembly; removing said driven axlesystem from a front position in said vehicle frame; installing said tagaxle system, including said differential assembly and said axle shafts,into said front position in said vehicle frame and attaching saiddifferential assembly to said drive shaft; and installing said drivenaxle system into said rear position on said vehicle frame and connectingsaid driven axle system to said differential assembly of said tag axlesystem.
 14. The method of claim 13, wherein said tag axle system has abowl with two hollow, radially extending arms and wherein said firstaxle shaft and said second axle shaft are located within said arms. 15.The method of claim 13, wherein an interaxle drive shaft connects saiddifferential of said tag axle system in said front position and saiddriven axle system in said rear position.
 16. The method of claim 15,wherein said drive shaft transmits torque from said engine to saiddifferential assembly in said front position for driving said axles andwhere some of said torque is provided through said interaxle drive shaftto said driven axle system in said rear position.
 17. The method ofclaim 13, wherein said tag axle system and said driven axle system aresubstantially similar in shape and size.